Electronic ignition systems of internal combustion motors are commonly used, which systems may be divided into two groups. In the first group there are the so-called thyristor or capacitive ignition systems; in such a system a capacitor will be charged and the stored energy of this capacitor will be switched on the primary winding of the high voltage transformer by means of a thyristor at the instant of the ignition. The advantage of such systems is that the contact breaker, which controls the instant of the ignition, switches very small current only, therefore the lifetime of the contact breaker increases. The drawback of such systems is however that an inverter is needed to charge the capacitor, which owing to its structure needs many components, is expensive, and during the short time between two pulses only a limited amount of energy can be stored in the capacitor at acceptable cost.
To the second group of electronic ignition systems belong the so-called transistor ignition systems; in such a system not a contact breaker, but a switching transistor circuit is serial connected to the primary winding of a conventional ignition coil. In such a system the contact breaker is disburdened too, since it generates a control pulse of very small current only and a switching transistor is used to interrupt the high current of the primary winding. The advantages of such a system is the disburdening of the contact breaker, and that higher current pulses can be interrupted in the primary winding of the ignition coil.
It is well known that the quality of the combustion in an internal combustion motor as well as the efficiency of the motor can be improved in that way that the ignition of the fuel will be effected more perfectly, and this is possible by increasing the energy of the ignition spark.
As we mentioned, in capacitive ignition systems the increasing of the energy of the spark is limited by the complexity and costs of the system. The energy converting efficiency of transistor ignition systems is relatively low. The energy of the high voltage pulse as well as that of the spark changes significantly with the change of the supply voltage, and this hampers especially the cold starting of internal combustion motors of vehicles. As it is well known, at cold starting the starting electric motor reduces the voltage of the cold start battery to such an extent that this reduced battery voltage is frequently not enough to generate the ignition spark.
It is the aim of the Hungarian Pat. No. 186,116. "Circuit arrangement for generating high voltage pulses" to eliminate these drawbacks, in which the primary winding of the high voltage transformer is divided into two winding parts. In this known circuit one of the primary windings of the transformer as well as a switching circuit and a capacitor form together a loop circuit. Both primary windings are serial connected and over a diode they are connected to a voltage source. The operation principle of this circuit is that at the instant of switching on the switching transistor forming a switching circuit the stored energy of the capacitor drives current through one of the primary windings of the transformer, which current adds itself to the current flowing from the voltage source and by this way a significantly higher current pulse can be generated through the primary winding.
It is the advantage of this circuit that at the interrupting of the current flowing through the primary winding, that is when the switching transistor switches off, the voltage arising in the other primary winding with opposite polarity and charges the capacitor. In this way this is an energy recovery circuit, since the induced voltage arising at the interruption of the current charges over the energy stored in the transformer into the capacitor. In this way this is an energy recovery circuit. Although this circuit worked well in the practice, the winding used to energy recovery does not work at generating the spark.
In the circuit arrangements described above theoretically electromechanical switching devices could also be used as switching circuits, yet these have so many drawbacks that in electronic ignition systems they are used at most as control switches. To interrupt the high current flowing through the primary winding of the transformer high power switching transistors come above all into consideration. I have used such a transistor in the ignition system according to my above mentioned Hungarian Pat. No. 186,116. In this known circuit the switching transistor is actuated by a transistor amplifier, which is controlled by a control circuit. A negative feedback circuit is applied comprising a voltage dependent resistor so that lest the changing, first of all the reduction of the supply voltage may significantly reduce the energy of the pulse. This voltage dependent resistor - taking into consideration the low supply voltage, the needed characteristic and the value of the resistor - should be an incandescent lamp, yet the dimensions, lifetime and reliability of which are disadvantageous compared to other components, and this is why the practical applicability of this circuit arrangement is limited.
The invention has for its object to provide a circuit arrangement described in the opening paragraph, which should combine the advantages of both the capacitive and the transistor ignition systems; moreover the stored magnetic energy should be recoverable with the best possible efficiency and by this way the efficiency of the generating the high voltage pulse should be improved. Another aim of the invention was to form such a switching circuit, by means of which the energy of the high voltage impulse could be kept constant under a supply voltage changing within broad limits, what would be very advantageous especially to cold starting of internal combustion motors of vehicles.